What proportion of people with autism have a large head? When Leo Kanner first described 11 children with autism in a 1943 paper, he noted many unusual features. “Five had relatively large heads,” he reported, and he said no more on the matter. But the sample size was small.
Many other scientists noted the same link over the following decades. A 1999 review estimated that 20 percent of people with autism have statistically large head size, or ‘macrocephaly’1.
Do autistic children who have alarge head also have a large brain? Yes. Researchers have scanned the brains of autistic people by using technologies such as magnetic resonance imaging (MRI) and have found that those with a large head also tend to have an unusually large brain. However, the link between the two is not entirely straightforward — some autistic children with an enlarged brain don’t have a large head — so it is best for researchers to scan the brain rather than rely on head measurements.